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Abstract:

A method for manufacturing an oxide thin film transistor with leakage
currents less than 10-14 angstrom includes the steps of forming an
oxide semiconductor active layer by a deposition process. In the
deposition process, an electric power is in a range from 1.5 kilowatts to
10 kilowatts. The oxide thin film transistor manufactured by the above
methods has advantages of low leakage currents, high electron mobility,
and excellent temperature stability. The present invention also provides
a method for manufacturing a display device. The display quality of the
display device can be improved.

Claims:

1. A method for manufacturing an oxide thin film transistor with leakage
currents less than 10.sup.-14 angstrom, comprising: forming an oxide
semiconductor active layer by a deposition process, wherein a gas used in
the deposition process comprises oxygen with a flow ratio to the total
gas in a range from 4% to 20%.

2. The method for manufacturing an oxide thin film transistor as claimed
in claim 1, wherein the deposition process is a sputtering deposition
process.

4. The method for manufacturing an oxide thin film transistor as claimed
in claim 1, wherein a thickness of the oxide semiconductor active layer
is in a range from 300 angstroms to 2000 angstroms.

5. The method for manufacturing an oxide thin film transistor as claimed
in claim 1, wherein the gas used in the deposition process further
comprises argon.

6. The method for manufacturing an oxide thin film transistor as claimed
in claim 1, wherein an electric power used in the deposition process is
in range from 1.5 kilowatts to 10 kilowatts.

7. A method for manufacturing an oxide thin film transistor with leakage
currents less than 10.sup.-14 angstrom, comprising: forming an oxide
semiconductor active layer with a thickness in a range from 300 angstroms
to 2000 angstroms by a deposition process.

8. The method for manufacturing an oxide thin film transistor as claimed
in claim 6, wherein the deposition process is a sputtering deposition
process.

10. The method for manufacturing an oxide thin film transistor as claimed
in claim 6, wherein an electric power used in the deposition process is
in range from 1.5 kilowatts to 10 kilowatts.

11. A method for manufacturing an oxide thin film transistor with leakage
currents less than 10.sup.-14 angstrom, comprising: forming an oxide
semiconductor active layer by a deposition process, wherein an electric
power used in the deposition process is in range from 1.5 kilowatts to 10
kilowatts.

12. The method for manufacturing an oxide thin film transistor as claimed
in claim 11, wherein the deposition process is a sputtering deposition
process.

Description:

[0001] This application is a continuation application of an application
Ser. No. 12/699,063, filed on Feb. 3, 2010, and the entire contents of
which are incorporated herein by reference.

BACKGROUND

[0002] 1. Field of the Invention

[0003] The present invention relates to a method for manufacturing a thin
film transistor, and more particularly to a method for manufacturing an
oxide thin film transistor.

[0004] 2. Description of the Related Art

[0005] In these days, thin film transistor display devices, such as liquid
crystal display devices, electrophoretic display devices and organic
light emitting diode display devices, have been used more and more
widely. To improve display quality of the display devices, people have
always paid attention to research and development of structure and
manufacturing method of a thin film transistor (TFT) that is one of core
structure of the display device.

[0006] A conventional thin film transistor has an active layer made of
amorphous silicon (a-Si). However, the conventional thin film transistor
has some shortcomings, such as high leakage currents, low electron
mobility and some of functions of integrated circuit incapable of forming
on a substrate directly. Therefore, the conventional thin film transistor
fails to satisfy the needs of high display quality of the display
devices. For solving the above problems, low temperature polysilicon
(LTPS) can be used to make the active layer. However, the process of
making the low temperature polysilicon is complicated and has a low
product yield, thus the low temperature polysilicon is still not easily
to be used widely. Recently, an oxide thin film transistor appears, which
has an active layer made of an oxide semiconductor, and can overcomes the
above mentioned problems.

[0007] However, it is a new application that the oxide semiconductor is
used for the active layer of the oxide thin film transistor. Therefore,
some topics, such as, how to manufacture the oxide thin film transistor
with good performances, are still in research stages.

[0008] What is needed, therefore, is a new method for manufacturing an
oxide thin film transistor and a new method for manufacturing a display
device that can overcome the above-mentioned shortcomings.

BRIEF SUMMARY

[0009] The present invention relates to a method for manufacturing an
oxide thin film transistor, where the oxide thin film transistor has
advantages of low leakage currents, high electron mobility and excellent
temperature stability.

[0010] To achieve the above-mentioned advantage, the present invention
provides a method for manufacturing an oxide thin film transistor with
leakage currents less than 10-14 angstrom. The method includes the
steps of forming an oxide semiconductor active layer by a deposition
process. In the deposition process, a gas used includes oxygen with a
flow ratio to the total gas in a range from 4% to 20%.

[0011] To achieve the above-mentioned advantage, the present invention
provides a method for manufacturing an oxide thin film transistor with
leakage currents less than 10-14 angstrom. The method includes the
steps of forming an oxide semiconductor active layer with a thickness in
a range from 300 angstroms to 2000 angstroms by a deposition process.

[0012] To achieve the above-mentioned advantage, the present invention
provides a method for manufacturing an oxide thin film transistor with
leakage currents less than 10-14 angstrom. The method includes the
steps of forming an oxide semiconductor active layer by a deposition
process. In the deposition process, an electric power is in a range from
1.5 kilowatts to 10 kilowatts.

[0014] In the method for manufacturing the oxide thin film transistor of
the present invention, the oxide semiconductor active layer is formed by
the deposition process. In the deposition process, an electric power is
in the range from 1.5 kilowatts to 10 kilowatts, so that suitable plasma
can be produced to deposit an oxide semiconductor. The oxide thin film
transistor that is manufactured by the above methods has advantages of
low leakage currents, high electron mobility, and excellent temperature
stability. And thus, if the oxide thin film transistor is used in the
display device, the display device can have an improved display quality.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] These and other features and advantages of the various embodiments
disclosed herein will be better understood with respect to the following
description and drawings, in which like numbers refer to like parts
throughout, and in which:

[0016] FIG. 1 is a schematic, side cross-sectional view of a display
device according to a first embodiment of the present invention.

[0017]FIG. 2 is a flow chart of the method for manufacturing the display
device of FIG. 1.

[0018]FIG. 3 is a curve graph of drain current and gate voltage of an
oxide thin film transistor according to the present invention.

[0019]FIG. 4 is a schematic, side cross-sectional view of a display
device according to a second embodiment of the present invention.

DETAILED DESCRIPTION

[0020] A display device includes a plurality of pixels. Structures of the
pixels are substantially the same with each other; therefore, only one
pixel would be shown illustratively to present the all pixels of the
display device in the following drawings.

[0021] FIG. 1 is a schematic, side cross-sectional view of a display
device according to a first embodiment of the present invention.
Referring to FIG. 1, the display device 100 can be, but not limited to,
an electrophoretic display device. In this embodiment, the display device
100 includes a substrate 110, an oxide thin film transistor array (not
labeled) formed on the substrate 110 and a display layer 130 disposed on
the oxide thin film transistor array. The oxide thin film transistor
array can include a plurality of oxide thin film transistors 120, and
only one of the oxide thin film transistors 120 is shown illustratively
in FIG. 1.

[0022] A method for manufacturing the display device 100 would be
described detailedly below. It should be noted that, the following
description of the method for manufacturing the display device 100 is not
limitation. For example, the various steps in the method may be arranged
in a different sequence to achieve a similar effect.

[0023]FIG. 2 is a flow chart of the method for manufacturing the display
device 100 of FIG. 1. Referring to FIG. 2, firstly, at step 10, a
substrate 110 is provided. The substrate 110 can be a transparent glass
substrate or an acrylic substrate. In this embodiment, a surface of the
substrate 110 is mainly used to form an oxide thin film transistor array
thereon.

[0024] At steps 11 to 14, the oxide thin film transistor array is formed
on the surface of the substrate 110. In detail, at step 11, a gate 121 is
formed on the surface of the substrate 110. At step 12, a gate insulating
layer 122 is formed on the gate 121, so as to cover the gate 121. At step
13, an oxide semiconductor active layer 123 is formed on the gate
insulating layer 122 by a deposition process. At step 14, a source 124
and a drain 125 are formed on the gate insulating layer 122, and the
source 124 and the drain 125 are electrically connected with the oxide
semiconductor active layer 123 respectively. As such, the oxide thin film
transistor 120 is made. Material of the oxide semiconductor active layer
123 can be selected from the group consisting of zinc oxide (ZnO), zinc
tin oxide (ZnSnO), chromium zinc oxide (CrSnO), gallium zinc oxide
(GaSnO), titanium zinc oxide (TiSnO), indium gallium zinc oxide (InGaZnO
, IGZO), copper aluminum oxide (CuAlO), strontium copper oxide (SrCuO),
lanthanum copper oxide (LaCuOS) and any suitable combination thereof. In
this embodiment, the oxide semiconductor active layer 123 is made of
indium gallium zinc oxide, and the following process of manufacturing the
oxide semiconductor active layer 123 is described by taking indium
gallium zinc oxide as an example.

[0025] In detail, when the oxide semiconductor active layer 123 is formed
by the deposition process, a total flow rate of a gas can be more than
100 standard cubic centimeters per minute (sccm) and an electric power
can be in a range from 1.5 kilowatts to 10 kilowatts, so that suitable
plasma can be produced to deposit an oxide semiconductor. The gas can
include oxygen (O2) and argon (Ar). A flow ratio of oxygen to the
total gas can be in a range from 4% to 20%. A thickness of the oxide
semiconductor active layer 123 can be in a range from 300 angstroms to
2000 angstroms. In this embodiment, the oxide semiconductor active layer
123 can be, but not limited to, formed by a sputtering deposition
process.

[0026] Referring to FIG. 2, after the source 124 and the drain 125 is
formed, at step 15, a protection film 126 and a resin layer 127 can be
formed on the source 124 and the drain 125, and a pixel electrode 128 can
be formed to electrically connect to the drain 125.

[0027] In this embodiment, the oxide thin film transistor 120 is a bottom
gate type. In an alternative embodiment, the oxide thin film transistor
120 can be a top gate type. Relative to the top bottom gate type, when
the oxide thin film transistor 120 is the top gate type, an order of
forming the various electrodes has a little difference, but the process
of forming the oxide semiconductor active layer 123 is the same.

[0028] Referring to FIG. 2, at steps 16, a display layer 130 is disposed
on the oxide thin film transistor array. In this embodiment, the display
layer 130 is an electrophoretic display layer. The electrophoretic
display layer can be a microcapsule electrophoretic display layer or a
microcup electrophoretic display layer. In addition, a color filter (not
shown) can further be disposed on the display layer 130, so that the
display device 100 may achieve color display. It should be understood
that, the method for manufacturing the display device 100 may further
including disposing a protecting layer 140 to seal the display device
100, configuring an integrated circuit, and connecting to a printed
circuit board (not shown).

[0029] In this embodiment, the oxide semiconductor active layer 123 of the
oxide thin film transistor 120 is formed by the deposition process. By
controlling the conditions of deposition process, the oxide thin film
transistor 120 with good performances can be obtained easily. FIG. 3 is a
curve graph of drain current and gate voltage (Id-Vg) of the oxide thin
film transistor 120, wherein, the drain voltages (Vd) are 0.1 volt (V),
9.9V and 5V respectively. The performances of the oxide thin film
transistor 120 manufactured by the above methods can keep stability,
after being heated at 200 Celsius degree for two hours. In other words,
the reliability of the oxide thin film transistor 120 can not be
influenced easily by temperature, and the oxide thin film transistor 120
has excellent temperature stability. In addition, leakage currents of the
oxide thin film transistor 120 can be less than 10-14, and even if
the oxide thin film transistor 120 is under sunlight or ultraviolet
radiation, the leakage currents would still not increase. Electron
mobility of the oxide thin film transistor 120 can be 2 square
centimeters per volt per second (cm2/V sec). Therefore, the oxide
thin film transistor 120 has advantages of low leakage currents, high
electron mobility, and excellent temperature stability. And thus, when
the oxide thin film transistor 120 is used in the display device 100, the
display device 100 can have an improved display quality.

[0030]FIG. 4 is a schematic, side cross-sectional view of a display
device according to a second embodiment of the present invention.
Referring to FIG. 4, the display device 100a can be, but not limited to,
a liquid crystal display device. In this embodiment, the method for
manufacturing the display device 100a is similar to that of the method
for manufacturing the display device 100 of the first embodiment. The
difference is that an oxide thin film transistor 120a is a top gate type.
A process of forming an oxide semiconductor active layer 123a can be the
same to that of the oxide semiconductor active layer 123 of the oxide
thin film transistor 120, but the order of forming the various layers in
the oxide thin film transistor 120a has a little difference.

[0031] In detail, the oxide thin film transistor 120a is formed by the
following steps. Firstly, a source 124a and a drain 125a are formed on a
surface of the substrate 110a. Secondly, an oxide semiconductor active
layer 123a is formed on the surface of the substrate 110a by a deposition
process, and the oxide semiconductor active layer 123a is electrically
connected with the source 124a and the drain 125a respectively. Thirdly,
a gate insulating layer 122a is formed on the source 124a, the drain 125a
and the oxide semiconductor active layer 123a, so as to cover the source
124a, the drain 125a and the oxide semiconductor active layer 123a.
Fourthly, a gate 121a is formed on the gate insulating layer 122a, and
corresponds to the oxide semiconductor active layer 123a. Fifthly, an
insulation protection film 126a is formed on the gate 121a. As such, the
oxide thin film transistor 120a is made.

[0032] It should be understood that, for manufacturing the display device
100a, a pixel electrode 128a should be formed to electrically connect to
the drain 125a, and some other layers may be configured according to the
requirement of the display device 100a. In particular, a display layer
130a of the display device 100a is a liquid crystal display layer, and a
cell gap of the liquid crystal display layer can be in a range from 3
micrometers to 6 micrometers. Furthermore, a color filter substrate that
includes an alignment film 150, a common electrode 160, a color filter
layer 170, an insulation protection film 126a and an upper substrate 180
formed on the display layer 130a in the above mentioned order, is
configured so as to make the display device 100a achieve display. In
addition, for manufacturing the display device 100a, steps of configuring
an integrated circuit (not shown) and connecting with the printed circuit
board (not shown) may also be required.

[0033] It should be noted that, the display layer of the display device
can be other display layers, such as an organic light emitting diode
display layer. When the display layer is the organic light emitting diode
display layer, the oxide thin film transistor can be a bottom gate type
or a top gate type, and the method for manufacturing the display device
should be modified properly. The organic light emitting diode display
layer can be bottom-emitting or top-emitting.

[0034] In summary, in the method for manufacturing the oxide thin film
transistor and the method for manufacturing the display device of the
present invention, the oxide semiconductor active layer is formed by the
deposition process. In the deposition process, a total flow rate of a gas
is more than 100 standard cubic centimeters per minute and an electric
power is in the range from 1.5 kilowatts to 10 kilowatts, so that
suitable plasma can be produced to deposit an oxide semiconductor. The
oxide thin film transistor that is manufactured by the above methods has
low leakage currents, high electron mobility, and excellent temperature
stability. And thus, when the oxide thin film transistor is used in the
display device, the display device can have an improved display quality.

[0035] The above description is given by way of example, and not
limitation. Given the above disclosure, one skilled in the art could
devise variations that are within the scope and spirit of the invention
disclosed herein, including configurations ways of the recessed portions
and materials and/or designs of the attaching structures. Further, the
various features of the embodiments disclosed herein can be used alone,
or in varying combinations with each other and are not intended to be
limited to the specific combination described herein. Thus, the scope of
the claims is not to be limited by the illustrated embodiments.